This is on Plasma 6.
KDE Plasma Version: 6.3.4
KDE Frameworks Version: 6.12.0
My Dolphin bookmarks disappeared. I just noticed that the location of Dolphin’s bookmarks.xml file has changed.
The old location is: ~/.local/share/dolphin/
The new location is: ~/.local/share/kfile/
I just copied my old bookmarks.xml file to the new location and that brought them back. The last time my old bookmarks file was written to was 3/20/2025, so I really don’t know when it changed, but it was after that date. I did compare the file formats and it appears that nothing changed except for where it stores and looks for the bookmarks.xml file.